The present invention relates to data communications and telecommunications generally, and, in particular, to high speed data transmission over copper telephony wires.
The term xe2x80x9cloopxe2x80x9d is used throughout the specification and claims to mean a single twisted pair of copper wires suitable for voice. The term xe2x80x9cvoice/data devicexe2x80x9d is intended to mean any telephone, facsimile machine, or other POTs or ISDN device which transmits voice/data along subscriber loops in the frequency band 0-80 kHz.
The need to transmit data at high speed over copper wires, by use of various digital subscriber line technologies, is well known. Many businesses and public institutions are well serviced by purpose built local area networks (LANs) for the internal high speed transmission of data.
LANs are often constructed on the basis of twisted pairs of high grade, so-called xe2x80x9ccategory 5xe2x80x9d copper wares. Among standard protocols for data transmission along LANs are the well known packet data communications standard IEEE802.3 and Ethernet. By use of this high quality wiring, Ethernet is employed to transmit data signals at a rate of more than 100 MB per second. Accordingly, LANs are commonly used to connect various network devices and personal computers (PCs), referred to herein collectively as xe2x80x9cnodes,xe2x80x9d to a central Ethernet hub or switch, by use of a star topology.
It will thus be appreciated that connection of a high speed direct connection to an Internet or other high speed data provider, referred to herein collectively as xe2x80x9cISPs,xe2x80x9d inherently provides each node on the network with equally high speed data connectivity to the ISP.
Residential and older office buildings, however, provide a challenge to high quality data transmission, as they normally have relatively low quality copper lines which, apart from being low grade, often category 3 or less, are sought to be used also for traditional voice telephony by means of various active devices such as telephones and fax machines, and will also have many internal connections and splits. Furthermore, while many telephone lines are provided with two or four twisted pairs, so as to enable the use of voice and data connections at the same time, many are provided with single loops, preventing simultaneous use of the line for both voice and data transmission.
Use of existing copper wires in LAN-less environments normally provides a low quality connection due to the presence of multiple connections in the wiring, each connection causing the reflection of electrical signals that create echoes, thereby degrading the quality of reception. The presence of analog voice devices on the lines also occupies a certain amount of the available bandwidth, thereby reducing the bandwidth available far data transmission.
Various solutions for enabling the use of subscriber loops simultaneously for voice and data have been suggested, although they generally involve the use of a splitter, which has the effect of rendering the cost of such systems relatively high. Echo cancellation may also be required, and crosstalk, which occurs in bundled lines extending from the central office of the telephone company to the Punch Down Block (PDB), particularly on high speed DSL services, is also a problem that must be overcome. As known, the (PDB) may be located at any suitable location, such as, in a street cabinet, the basement of an apartment building, or the like.
A splitterless solution that is known in the art, is the so-called xe2x80x9cG Litexe2x80x9d standard for Splitterless Asymmetrical Digital Subscriber Line Transceivers. While this clearly does not have the drawbacks of systems requiring the use of splitters it still does not overcome the problem of switching of analog voice devices during use of the line for data communications. In other words, while the use of a copper line for data and voice simultaneously is not a problem, per se, the switching of a telephone, namely, the picking up or replacing of the telephone handset while the line is connected to a data source, such as an ISP, can cause interference to or loss of communication between an end unit such as a PC, and the data source.
Furthermore, many of the high speed solutions to provision of a high data transmission rate related to the provision of data over subscriber loops extending from the central office of the telephone company to the PDB, and thus to the ability to provide data over distances of as much as 20,000 feet or more. Necessarily, these solutions must deal With many problems that arise specifically from the long distance over which the data must be transmitted along telephone lines.
The present invention seeks to provide a splitterless system for providing 10 MB/sec half/full duplex Ethernet quality data communications via a subscriber loop, wherein the quality of the data transmission is not significantly affected by the simultaneous use of voice/data devices, including POTs. ISDN, telephone and facsimile machines, on the same line. Specifically, the data transmission is not significantly affected either by voice data or by switching of an analog voice device.
A further aim of the present invention is to provide a system which provides Ethernet quality data communications along subscriber loops and is independent of the distance of the subscriber from the telephone company, thereby to overcome problems of known art caused specifically by the necessity of high speed transmission of data over long distances.
Specifically, as will be appreciated from the following description, the system of the present invention is suitable for use with any of the following wiring arrangements:
1. A single loop with a resident voice/data device.
2. A single loop dedicated to data.
3. A pair of loops dedicated to data, providing complete physical separation between uplinking and downlinking.
There is thus provided, an accordance with a preferred embodiment of the present invention, a splitterless system for providing along a subscriber loop, full Ethernet wire speed data transmission between a data source and an Ethernet standard end device. The system includes a gateway modem device connected to a data source, and arranged in splitterless contact with a subscriber loop extending between a Punch Down Block (PDB), and an Ethernet standard end device; and a user modem device connected between the Ethernet standard end device and the subscriber loop so as to define with the gateway modem device a subscriber loop segment wherein the gateway modem device and the user modem device are operative to communicate along the loop segment in different predetermined, first and second frequency spectra, for uplinking and downlinking, respectively, thus to facilitate therealong full Ethernet wire speed data transmission therealong.
Additionally in accordance with a preferred embodiment of the invention, the gateway modem device and the user modem device are operative to communicate in frequency spectra predetermined so as to facilitate full coexistence on the loop with a voice/data device.
Preferably, the gateway modem device and the user modem device are operative to communicate in a frequency spectra having a predetermined minimum value which is greater than that at which the signal to noise ratio (SNR) is greater than or equal to a predetermined minimum value, typically 24 DB, even in the presence of a switching signal caused by a hook on/off action of a voice/data device.
Further in accordance with a preferred embodiment of the invention, the maximum value of the first frequency spectrum for uplinking is no greater than the minimum value of the second frequency spectrum for down linking, wherein, in a case in which no coexistence with voice/data devices is required, the first frequency spectrum is typically in the range 0-4.0 MHz, but more preferably in the range 200 kHz-3.0 MHz, and the second frequency spectrum is in the range 4.0-10.0 MHz, but more preferably in the range 6.0-9.0 MHz.
In a case where coexistence is required, however, the first frequency spectrum is in the range 1.0-4.0 MHz, and the second frequency spectrum is in the range 6.0-9.0 MHz.
Additionally in accordance with a preferred embodiment of the invention, there is also provided apparatus, associated with the gateway modem device, the loop segment, the user modem device and the end unit, for providing along the loop segment a first impedance in response to transmission in the first frequency spectrum, and a second impedance in response to reception In the second frequency spectrum, thereby to provide an unmatched system and thus to reduce a loss in transmission power that occurs in the presence of a change in system impedance caused by a hook on/off action of a voice/data device.
Preferably, the system impedance is less than the matched impedance of the loop segment such that, in a matched system whose impedance is 100 xcexa9, the impedance provided by the apparatus for providing an impedance is no greater than 93 xcexa9, and preferably is approximately 80 xcexa9.
Further in accordance with a preferred embodiment of the invention, the user modem includes apparatus for preventing entry into the modem of ringing voltages of analog/voice devices; and apparatus for preventing entry into the modem of switching voltages, thereby to prevent loss of locking between the user modem and the gateway modem.
Additionally in accordance with a preferred embodiment of the invention, the user modem includes apparatus for transmitting a disconnect signal to the gateway modem upon switching off of the user modem, and wherein, in the presence of user modem initiated a line break of greater than a predetermined time period, in the absence of receipt of the disconnect signal, the gateway modem is operative to provide an alarm signal.
Further in accordance with a preferred embodiment of the invention, the gateway modem device is a multiple modem unit for splitterless connection to a plurality of subscriber loops extending from a common PDB, and wherein the plurality of subscriber loops are connected to a plurality of Ethernet standard end units via a corresponding plurality of the user modems; and the multiple modem unit and the user modems are operative to facilitate communications between the Ethernet standard end units, so as to form an Ethernet standard network thereamong.